Type Object Structures (original) (raw)

Perhaps one of the most important structures of the Python object system is the structure that defines a new type: the PyTypeObject structure. Type objects can be handled using any of the PyObject_* orPyType_* functions, but do not offer much that’s interesting to most Python applications. These objects are fundamental to how objects behave, so they are very important to the interpreter itself and to any extension module that implements new types.

Type objects are fairly large compared to most of the standard types. The reason for the size is that each type object stores a large number of values, mostly C function pointers, each of which implements a small part of the type’s functionality. The fields of the type object are examined in detail in this section. The fields will be described in the order in which they occur in the structure.

In addition to the following quick reference, the Examplessection provides at-a-glance insight into the meaning and use ofPyTypeObject.

Quick Reference¶

“tp slots”¶

PyTypeObject Slot [1]	Type	special methods/attrs	Info [2]
O	T	D	I
tp_name	const char *	__name__	X	X
tp_basicsize	Py_ssize_t	X	X	X
tp_itemsize	Py_ssize_t	X	X
tp_dealloc	destructor	X	X	X
tp_vectorcall_offset	Py_ssize_t	X	X
(tp_getattr)	getattrfunc	__getattribute__, __getattr__	G
(tp_setattr)	setattrfunc	__setattr__, __delattr__	G
tp_as_async	PyAsyncMethods *	sub-slots	%
tp_repr	reprfunc	__repr__	X	X	X
tp_as_number	PyNumberMethods *	sub-slots	%
tp_as_sequence	PySequenceMethods *	sub-slots	%
tp_as_mapping	PyMappingMethods *	sub-slots	%
tp_hash	hashfunc	__hash__	X	G
tp_call	ternaryfunc	__call__	X	X
tp_str	reprfunc	__str__	X	X
tp_getattro	getattrofunc	__getattribute__, __getattr__	X	X	G
tp_setattro	setattrofunc	__setattr__, __delattr__	X	X	G
tp_as_buffer	PyBufferProcs *	%
tp_flags	unsigned long	X	X	?
tp_doc	const char *	__doc__	X	X
tp_traverse	traverseproc	X	G
tp_clear	inquiry	X	G
tp_richcompare	richcmpfunc	__lt__, __le__, __eq__, __ne__, __gt__, __ge__	X	G
(tp_weaklistoffset)	Py_ssize_t	X	?
tp_iter	getiterfunc	__iter__	X
tp_iternext	iternextfunc	__next__	X
tp_methods	PyMethodDef []	X	X
tp_members	PyMemberDef []	X
tp_getset	PyGetSetDef []	X	X
tp_base	PyTypeObject *	__base__	X
tp_dict	PyObject *	__dict__	?
tp_descr_get	descrgetfunc	__get__	X
tp_descr_set	descrsetfunc	__set__, __delete__	X
(tp_dictoffset)	Py_ssize_t	X	?
tp_init	initproc	__init__	X	X	X
tp_alloc	allocfunc	X	?	?
tp_new	newfunc	__new__	X	X	?	?
tp_free	freefunc	X	X	?	?
tp_is_gc	inquiry	X	X
<tp_bases>	PyObject *	__bases__	~
<tp_mro>	PyObject *	__mro__	~
[tp_cache]	PyObject *
[tp_subclasses]	void *	__subclasses__
[tp_weaklist]	PyObject *
(tp_del)	destructor
[tp_version_tag]	unsigned int
tp_finalize	destructor	__del__	X
tp_vectorcall	vectorcallfunc
[tp_watched]	unsigned char

sub-slots¶

Slot	Type	special methods
am_await	unaryfunc	__await__
am_aiter	unaryfunc	__aiter__
am_anext	unaryfunc	__anext__
am_send	sendfunc
nb_add	binaryfunc	__add__ __radd__
nb_inplace_add	binaryfunc	__iadd__
nb_subtract	binaryfunc	__sub__ __rsub__
nb_inplace_subtract	binaryfunc	__isub__
nb_multiply	binaryfunc	__mul__ __rmul__
nb_inplace_multiply	binaryfunc	__imul__
nb_remainder	binaryfunc	__mod__ __rmod__
nb_inplace_remainder	binaryfunc	__imod__
nb_divmod	binaryfunc	__divmod__ __rdivmod__
nb_power	ternaryfunc	__pow__ __rpow__
nb_inplace_power	ternaryfunc	__ipow__
nb_negative	unaryfunc	__neg__
nb_positive	unaryfunc	__pos__
nb_absolute	unaryfunc	__abs__
nb_bool	inquiry	__bool__
nb_invert	unaryfunc	__invert__
nb_lshift	binaryfunc	__lshift__ __rlshift__
nb_inplace_lshift	binaryfunc	__ilshift__
nb_rshift	binaryfunc	__rshift__ __rrshift__
nb_inplace_rshift	binaryfunc	__irshift__
nb_and	binaryfunc	__and__ __rand__
nb_inplace_and	binaryfunc	__iand__
nb_xor	binaryfunc	__xor__ __rxor__
nb_inplace_xor	binaryfunc	__ixor__
nb_or	binaryfunc	__or__ __ror__
nb_inplace_or	binaryfunc	__ior__
nb_int	unaryfunc	__int__
nb_reserved	void *
nb_float	unaryfunc	__float__
nb_floor_divide	binaryfunc	__floordiv__
nb_inplace_floor_divide	binaryfunc	__ifloordiv__
nb_true_divide	binaryfunc	__truediv__
nb_inplace_true_divide	binaryfunc	__itruediv__
nb_index	unaryfunc	__index__
nb_matrix_multiply	binaryfunc	__matmul__ __rmatmul__
nb_inplace_matrix_multiply	binaryfunc	__imatmul__
mp_length	lenfunc	__len__
mp_subscript	binaryfunc	__getitem__
mp_ass_subscript	objobjargproc	__setitem__, __delitem__
sq_length	lenfunc	__len__
sq_concat	binaryfunc	__add__
sq_repeat	ssizeargfunc	__mul__
sq_item	ssizeargfunc	__getitem__
sq_ass_item	ssizeobjargproc	__setitem__ __delitem__
sq_contains	objobjproc	__contains__
sq_inplace_concat	binaryfunc	__iadd__
sq_inplace_repeat	ssizeargfunc	__imul__
bf_getbuffer	getbufferproc()
bf_releasebuffer	releasebufferproc()

slot typedefs¶

typedef	Parameter Types	Return Type
allocfunc	PyTypeObject * Py_ssize_t	PyObject *
destructor	PyObject *	void
freefunc	void *	void
traverseproc	PyObject * visitproc void *	int
newfunc	PyTypeObject * PyObject * PyObject *	PyObject *
initproc	PyObject * PyObject * PyObject *	int
reprfunc	PyObject *	PyObject *
getattrfunc	PyObject * const char *	PyObject *
setattrfunc	PyObject * const char * PyObject *	int
getattrofunc	PyObject * PyObject *	PyObject *
setattrofunc	PyObject * PyObject * PyObject *	int
descrgetfunc	PyObject * PyObject * PyObject *	PyObject *
descrsetfunc	PyObject * PyObject * PyObject *	int
hashfunc	PyObject *	Py_hash_t
richcmpfunc	PyObject * PyObject * int	PyObject *
getiterfunc	PyObject *	PyObject *
iternextfunc	PyObject *	PyObject *
lenfunc	PyObject *	Py_ssize_t
getbufferproc	PyObject * Py_buffer * int	int
releasebufferproc	PyObject * Py_buffer *	void
inquiry	PyObject *	int
unaryfunc	PyObject *	PyObject *
binaryfunc	PyObject * PyObject *	PyObject *
ternaryfunc	PyObject * PyObject * PyObject *	PyObject *
ssizeargfunc	PyObject * Py_ssize_t	PyObject *
ssizeobjargproc	PyObject * Py_ssize_t PyObject *	int
objobjproc	PyObject * PyObject *	int
objobjargproc	PyObject * PyObject * PyObject *	int

See Slot Type typedefs below for more detail.

PyTypeObject Definition¶

The structure definition for PyTypeObject can be found inInclude/cpython/object.h. For convenience of reference, this repeats the definition found there:

typedef struct _typeobject { PyObject_VAR_HEAD const char tp_name; / For printing, in format "." / Py_ssize_t tp_basicsize, tp_itemsize; / For allocation */

/* Methods to implement standard operations */

destructor tp_dealloc;
Py_ssize_t tp_vectorcall_offset;
getattrfunc tp_getattr;
setattrfunc tp_setattr;
PyAsyncMethods *tp_as_async; /* formerly known as tp_compare (Python 2)
                                or tp_reserved (Python 3) */
reprfunc tp_repr;

/* Method suites for standard classes */

PyNumberMethods *tp_as_number;
PySequenceMethods *tp_as_sequence;
PyMappingMethods *tp_as_mapping;

/* More standard operations (here for binary compatibility) */

hashfunc tp_hash;
ternaryfunc tp_call;
reprfunc tp_str;
getattrofunc tp_getattro;
setattrofunc tp_setattro;

/* Functions to access object as input/output buffer */
PyBufferProcs *tp_as_buffer;

/* Flags to define presence of optional/expanded features */
unsigned long tp_flags;

const char *tp_doc; /* Documentation string */

/* Assigned meaning in release 2.0 */
/* call function for all accessible objects */
traverseproc tp_traverse;

/* delete references to contained objects */
inquiry tp_clear;

/* Assigned meaning in release 2.1 */
/* rich comparisons */
richcmpfunc tp_richcompare;

/* weak reference enabler */
Py_ssize_t tp_weaklistoffset;

/* Iterators */
getiterfunc tp_iter;
iternextfunc tp_iternext;

/* Attribute descriptor and subclassing stuff */
struct PyMethodDef *tp_methods;
struct PyMemberDef *tp_members;
struct PyGetSetDef *tp_getset;
// Strong reference on a heap type, borrowed reference on a static type
struct _typeobject *tp_base;
PyObject *tp_dict;
descrgetfunc tp_descr_get;
descrsetfunc tp_descr_set;
Py_ssize_t tp_dictoffset;
initproc tp_init;
allocfunc tp_alloc;
newfunc tp_new;
freefunc tp_free; /* Low-level free-memory routine */
inquiry tp_is_gc; /* For PyObject_IS_GC */
PyObject *tp_bases;
PyObject *tp_mro; /* method resolution order */
PyObject *tp_cache;
PyObject *tp_subclasses;
PyObject *tp_weaklist;
destructor tp_del;

/* Type attribute cache version tag. Added in version 2.6 */
unsigned int tp_version_tag;

destructor tp_finalize;
vectorcallfunc tp_vectorcall;

/* bitset of which type-watchers care about this type */
unsigned char tp_watched;

} PyTypeObject;

PyObject Slots¶

The type object structure extends the PyVarObject structure. Theob_size field is used for dynamic types (created by type_new(), usually called from a class statement). Note that PyType_Type (the metatype) initializes tp_itemsize, which means that its instances (i.e. type objects) must have the ob_size field.

Py_ssize_t PyObject.ob_refcnt¶

Part of the Stable ABI.

This is the type object’s reference count, initialized to 1 by thePyObject_HEAD_INIT macro. Note that for statically allocated type objects, the type’s instances (objects whose ob_typepoints back to the type) do not count as references. But fordynamically allocated type objects, the instances _do_count as references.

Inheritance:

This field is not inherited by subtypes.

PyTypeObject *PyObject.ob_type¶

Part of the Stable ABI.

This is the type’s type, in other words its metatype. It is initialized by the argument to the PyObject_HEAD_INIT macro, and its value should normally be&PyType_Type. However, for dynamically loadable extension modules that must be usable on Windows (at least), the compiler complains that this is not a valid initializer. Therefore, the convention is to pass NULL to thePyObject_HEAD_INIT macro and to initialize this field explicitly at the start of the module’s initialization function, before doing anything else. This is typically done like this:

Foo_Type.ob_type = &PyType_Type;

This should be done before any instances of the type are created.PyType_Ready() checks if ob_type is NULL, and if so, initializes it to the ob_type field of the base class.PyType_Ready() will not change this field if it is non-zero.

Inheritance:

This field is inherited by subtypes.

PyVarObject Slots¶

Py_ssize_t PyVarObject.ob_size¶

Part of the Stable ABI.

For statically allocated type objects, this should be initialized to zero. For dynamically allocated type objects, this field has a special internal meaning.

This field should be accessed using the Py_SIZE() andPy_SET_SIZE() macros.

Inheritance:

This field is not inherited by subtypes.

PyTypeObject Slots¶

Each slot has a section describing inheritance. If PyType_Ready()may set a value when the field is set to NULL then there will also be a “Default” section. (Note that many fields set on PyBaseObject_Typeand PyType_Type effectively act as defaults.)

const char *PyTypeObject.tp_name¶

Pointer to a NUL-terminated string containing the name of the type. For types that are accessible as module globals, the string should be the full module name, followed by a dot, followed by the type name; for built-in types, it should be just the type name. If the module is a submodule of a package, the full package name is part of the full module name. For example, a type namedT defined in module M in subpackage Q in package Pshould have the tp_name initializer "P.Q.M.T".

For dynamically allocated type objects, this should just be the type name, and the module name explicitly stored in the type dict as the value for key'__module__'.

For statically allocated type objects, the tp_name field should contain a dot. Everything before the last dot is made accessible as the __module__attribute, and everything after the last dot is made accessible as the__name__ attribute.

If no dot is present, the entire tp_name field is made accessible as the__name__ attribute, and the __module__ attribute is undefined (unless explicitly set in the dictionary, as explained above). This means your type will be impossible to pickle. Additionally, it will not be listed in module documentations created with pydoc.

This field must not be NULL. It is the only required field in PyTypeObject() (other than potentiallytp_itemsize).

Inheritance:

This field is not inherited by subtypes.

Py_ssize_t PyTypeObject.tp_basicsize¶

Py_ssize_t PyTypeObject.tp_itemsize¶

These fields allow calculating the size in bytes of instances of the type.

There are two kinds of types: types with fixed-length instances have a zerotp_itemsize field, types with variable-length instances have a non-zerotp_itemsize field. For a type with fixed-length instances, all instances have the same size, given in tp_basicsize. (Exceptions to this rule can be made usingPyUnstable_Object_GC_NewWithExtraData().)

For a type with variable-length instances, the instances must have anob_size field, and the instance size istp_basicsize plus N times tp_itemsize, where N is the “length” of the object.

Functions like PyObject_NewVar() will take the value of N as an argument, and store in the instance’s ob_size field. Note that the ob_size field may later be used for other purposes. For example, int instances use the bits ofob_size in an implementation-defined way; the underlying storage and its size should be accessed usingPyLong_Export().

Also, the presence of an ob_size field in the instance layout doesn’t mean that the instance structure is variable-length. For example, the list type has fixed-length instances, yet those instances have a ob_size field. (As with int, avoid reading lists’ ob_size directly. Call PyList_Size() instead.)

The tp_basicsize includes size needed for data of the type’stp_base, plus any extra data needed by each instance.

The correct way to set tp_basicsize is to use thesizeof operator on the struct used to declare the instance layout. This struct must include the struct used to declare the base type. In other words, tp_basicsize must be greater than or equal to the base’s tp_basicsize.

Since every type is a subtype of object, this struct must include PyObject or PyVarObject (depending on whether ob_size should be included). These are usually defined by the macro PyObject_HEAD orPyObject_VAR_HEAD, respectively.

The basic size does not include the GC header size, as that header is not part of PyObject_HEAD.

For cases where struct used to declare the base type is unknown, see PyType_Spec.basicsize and PyType_FromMetaclass().

Notes about alignment:

tp_basicsize must be a multiple of _Alignof(PyObject). When using sizeof on a struct that includesPyObject_HEAD, as recommended, the compiler ensures this. When not using a C struct, or when using compiler extensions like __attribute__((packed)), it is up to you.
If the variable items require a particular alignment,tp_basicsize and tp_itemsize must each be a multiple of that alignment. For example, if a type’s variable part stores a double, it is your responsibility that both fields are a multiple of_Alignof(double).

Inheritance:

These fields are inherited separately by subtypes. (That is, if the field is set to zero, PyType_Ready() will copy the value from the base type, indicating that the instances do not need additional storage.)

If the base type has a non-zero tp_itemsize, it is generally not safe to settp_itemsize to a different non-zero value in a subtype (though this depends on the implementation of the base type).

destructor PyTypeObject.tp_dealloc¶

A pointer to the instance destructor function. This function must be defined unless the type guarantees that its instances will never be deallocated (as is the case for the singletons None and Ellipsis). The function signature is:

void tp_dealloc(PyObject *self);

The destructor function is called by the Py_DECREF() andPy_XDECREF() macros when the new reference count is zero. At this point, the instance is still in existence, but there are no references to it. The destructor function should free all references which the instance owns, free all memory buffers owned by the instance (using the freeing function corresponding to the allocation function used to allocate the buffer), and call the type’stp_free function. If the type is not subtypable (doesn’t have the Py_TPFLAGS_BASETYPE flag bit set), it is permissible to call the object deallocator directly instead of viatp_free. The object deallocator should be the one used to allocate the instance; this is normally PyObject_Del() if the instance was allocated using PyObject_New or PyObject_NewVar, orPyObject_GC_Del() if the instance was allocated usingPyObject_GC_New or PyObject_GC_NewVar.

If the type supports garbage collection (has the Py_TPFLAGS_HAVE_GCflag bit set), the destructor should call PyObject_GC_UnTrack()before clearing any member fields.

static void foo_dealloc(foo_object *self) { PyObject_GC_UnTrack(self); Py_CLEAR(self->ref); Py_TYPE(self)->tp_free((PyObject *)self); }

Finally, if the type is heap allocated (Py_TPFLAGS_HEAPTYPE), the deallocator should release the owned reference to its type object (via Py_DECREF()) after calling the type deallocator. In order to avoid dangling pointers, the recommended way to achieve this is:

static void foo_dealloc(foo_object *self) { PyTypeObject *tp = Py_TYPE(self); // free references and buffers here tp->tp_free(self); Py_DECREF(tp); }

Warning

In a garbage collected Python, tp_dealloc may be called from any Python thread, not just the thread which created the object (if the object becomes part of a refcount cycle, that cycle might be collected by a garbage collection on any thread). This is not a problem for Python API calls, since the thread on which tp_dealloc is called will own the Global Interpreter Lock (GIL). However, if the object being destroyed in turn destroys objects from some other C or C++ library, care should be taken to ensure that destroying those objects on the thread which called tp_dealloc will not violate any assumptions of the library.

Inheritance:

This field is inherited by subtypes.

Py_ssize_t PyTypeObject.tp_vectorcall_offset¶

An optional offset to a per-instance function that implements calling the object using the vectorcall protocol, a more efficient alternative of the simpler tp_call.

This field is only used if the flag Py_TPFLAGS_HAVE_VECTORCALLis set. If so, this must be a positive integer containing the offset in the instance of a vectorcallfunc pointer.

The vectorcallfunc pointer may be NULL, in which case the instance behaves as if Py_TPFLAGS_HAVE_VECTORCALL was not set: calling the instance falls back to tp_call.

Any class that sets Py_TPFLAGS_HAVE_VECTORCALL must also settp_call and make sure its behaviour is consistent with the vectorcallfunc function. This can be done by setting tp_call to PyVectorcall_Call().

Changed in version 3.8: Before version 3.8, this slot was named tp_print. In Python 2.x, it was used for printing to a file. In Python 3.0 to 3.7, it was unused.

Changed in version 3.12: Before version 3.12, it was not recommended formutable heap types to implement the vectorcall protocol. When a user sets __call__ in Python code, only tp_call is updated, likely making it inconsistent with the vectorcall function. Since 3.12, setting __call__ will disable vectorcall optimization by clearing the Py_TPFLAGS_HAVE_VECTORCALL flag.

Inheritance:

This field is always inherited. However, the Py_TPFLAGS_HAVE_VECTORCALL flag is not always inherited. If it’s not set, then the subclass won’t usevectorcall, except whenPyVectorcall_Call() is explicitly called.

getattrfunc PyTypeObject.tp_getattr¶

An optional pointer to the get-attribute-string function.

This field is deprecated. When it is defined, it should point to a function that acts the same as the tp_getattro function, but taking a C string instead of a Python string object to give the attribute name.

Inheritance:

Group: tp_getattr, tp_getattro

This field is inherited by subtypes together with tp_getattro: a subtype inherits both tp_getattr and tp_getattro from its base type when the subtype’s tp_getattr and tp_getattro are both NULL.

setattrfunc PyTypeObject.tp_setattr¶

An optional pointer to the function for setting and deleting attributes.

This field is deprecated. When it is defined, it should point to a function that acts the same as the tp_setattro function, but taking a C string instead of a Python string object to give the attribute name.

Inheritance:

Group: tp_setattr, tp_setattro

This field is inherited by subtypes together with tp_setattro: a subtype inherits both tp_setattr and tp_setattro from its base type when the subtype’s tp_setattr and tp_setattro are both NULL.

PyAsyncMethods *PyTypeObject.tp_as_async¶

Pointer to an additional structure that contains fields relevant only to objects which implement awaitable and asynchronous iteratorprotocols at the C-level. See Async Object Structures for details.

Added in version 3.5: Formerly known as tp_compare and tp_reserved.

Inheritance:

The tp_as_async field is not inherited, but the contained fields are inherited individually.

reprfunc PyTypeObject.tp_repr¶

An optional pointer to a function that implements the built-in functionrepr().

The signature is the same as for PyObject_Repr():

PyObject *tp_repr(PyObject *self);

The function must return a string or a Unicode object. Ideally, this function should return a string that, when passed toeval(), given a suitable environment, returns an object with the same value. If this is not feasible, it should return a string starting with'<' and ending with '>' from which both the type and the value of the object can be deduced.

Inheritance:

This field is inherited by subtypes.

Default:

When this field is not set, a string of the form <%s object at %p> is returned, where %s is replaced by the type name, and %p by the object’s memory address.

PyNumberMethods *PyTypeObject.tp_as_number¶

Pointer to an additional structure that contains fields relevant only to objects which implement the number protocol. These fields are documented inNumber Object Structures.

Inheritance:

The tp_as_number field is not inherited, but the contained fields are inherited individually.

PySequenceMethods *PyTypeObject.tp_as_sequence¶

Pointer to an additional structure that contains fields relevant only to objects which implement the sequence protocol. These fields are documented in Sequence Object Structures.

Inheritance:

The tp_as_sequence field is not inherited, but the contained fields are inherited individually.

PyMappingMethods *PyTypeObject.tp_as_mapping¶

Pointer to an additional structure that contains fields relevant only to objects which implement the mapping protocol. These fields are documented inMapping Object Structures.

Inheritance:

The tp_as_mapping field is not inherited, but the contained fields are inherited individually.

hashfunc PyTypeObject.tp_hash¶

An optional pointer to a function that implements the built-in functionhash().

The signature is the same as for PyObject_Hash():

Py_hash_t tp_hash(PyObject *);

The value -1 should not be returned as a normal return value; when an error occurs during the computation of the hash value, the function should set an exception and return -1.

When this field is not set (and tp_richcompare is not set), an attempt to take the hash of the object raises TypeError. This is the same as setting it to PyObject_HashNotImplemented().

This field can be set explicitly to PyObject_HashNotImplemented() to block inheritance of the hash method from a parent type. This is interpreted as the equivalent of __hash__ = None at the Python level, causingisinstance(o, collections.Hashable) to correctly return False. Note that the converse is also true - setting __hash__ = None on a class at the Python level will result in the tp_hash slot being set toPyObject_HashNotImplemented().

Inheritance:

Group: tp_hash, tp_richcompare

This field is inherited by subtypes together withtp_richcompare: a subtype inherits both oftp_richcompare and tp_hash, when the subtype’stp_richcompare and tp_hash are both NULL.

Default:

PyBaseObject_Type uses PyObject_GenericHash().

ternaryfunc PyTypeObject.tp_call¶

An optional pointer to a function that implements calling the object. This should be NULL if the object is not callable. The signature is the same as for PyObject_Call():

PyObject *tp_call(PyObject *self, PyObject *args, PyObject *kwargs);

Inheritance:

This field is inherited by subtypes.

reprfunc PyTypeObject.tp_str¶

An optional pointer to a function that implements the built-in operationstr(). (Note that str is a type now, and str() calls the constructor for that type. This constructor calls PyObject_Str() to do the actual work, and PyObject_Str() will call this handler.)

The signature is the same as for PyObject_Str():

PyObject *tp_str(PyObject *self);

The function must return a string or a Unicode object. It should be a “friendly” string representation of the object, as this is the representation that will be used, among other things, by the print() function.

Inheritance:

This field is inherited by subtypes.

Default:

When this field is not set, PyObject_Repr() is called to return a string representation.

getattrofunc PyTypeObject.tp_getattro¶

An optional pointer to the get-attribute function.

The signature is the same as for PyObject_GetAttr():

PyObject *tp_getattro(PyObject *self, PyObject *attr);

It is usually convenient to set this field to PyObject_GenericGetAttr(), which implements the normal way of looking for object attributes.

Inheritance:

Group: tp_getattr, tp_getattro

This field is inherited by subtypes together with tp_getattr: a subtype inherits both tp_getattr and tp_getattro from its base type when the subtype’s tp_getattr and tp_getattro are both NULL.

Default:

PyBaseObject_Type uses PyObject_GenericGetAttr().

setattrofunc PyTypeObject.tp_setattro¶

An optional pointer to the function for setting and deleting attributes.

The signature is the same as for PyObject_SetAttr():

int tp_setattro(PyObject *self, PyObject *attr, PyObject *value);

In addition, setting value to NULL to delete an attribute must be supported. It is usually convenient to set this field toPyObject_GenericSetAttr(), which implements the normal way of setting object attributes.

Inheritance:

Group: tp_setattr, tp_setattro

This field is inherited by subtypes together with tp_setattr: a subtype inherits both tp_setattr and tp_setattro from its base type when the subtype’s tp_setattr and tp_setattro are both NULL.

Default:

PyBaseObject_Type uses PyObject_GenericSetAttr().

PyBufferProcs *PyTypeObject.tp_as_buffer¶

Pointer to an additional structure that contains fields relevant only to objects which implement the buffer interface. These fields are documented inBuffer Object Structures.

Inheritance:

The tp_as_buffer field is not inherited, but the contained fields are inherited individually.

unsigned long PyTypeObject.tp_flags¶

This field is a bit mask of various flags. Some flags indicate variant semantics for certain situations; others are used to indicate that certain fields in the type object (or in the extension structures referenced viatp_as_number, tp_as_sequence, tp_as_mapping, andtp_as_buffer) that were historically not always present are valid; if such a flag bit is clear, the type fields it guards must not be accessed and must be considered to have a zero or NULL value instead.

Inheritance:

Inheritance of this field is complicated. Most flag bits are inherited individually, i.e. if the base type has a flag bit set, the subtype inherits this flag bit. The flag bits that pertain to extension structures are strictly inherited if the extension structure is inherited, i.e. the base type’s value of the flag bit is copied into the subtype together with a pointer to the extension structure. The Py_TPFLAGS_HAVE_GC flag bit is inherited together with the tp_traverse and tp_clear fields, i.e. if thePy_TPFLAGS_HAVE_GC flag bit is clear in the subtype and thetp_traverse and tp_clear fields in the subtype exist and haveNULL values. .. XXX are most flag bits really inherited individually?

Default:

PyBaseObject_Type usesPy_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE.

Bit Masks:

The following bit masks are currently defined; these can be ORed together using the | operator to form the value of the tp_flags field. The macroPyType_HasFeature() takes a type and a flags value, tp and f, and checks whether tp->tp_flags & f is non-zero.

Py_TPFLAGS_HEAPTYPE¶

This bit is set when the type object itself is allocated on the heap, for example, types created dynamically using PyType_FromSpec(). In this case, the ob_type field of its instances is considered a reference to the type, and the type object is INCREF’ed when a new instance is created, and DECREF’ed when an instance is destroyed (this does not apply to instances of subtypes; only the type referenced by the instance’s ob_type gets INCREF’ed or DECREF’ed). Heap types should also support garbage collectionas they can form a reference cycle with their own module object.

Inheritance:

???

Py_TPFLAGS_BASETYPE¶

This bit is set when the type can be used as the base type of another type. If this bit is clear, the type cannot be subtyped (similar to a “final” class in Java).

Inheritance:

???

Py_TPFLAGS_READY¶

This bit is set when the type object has been fully initialized byPyType_Ready().

Inheritance:

???

Py_TPFLAGS_READYING¶

This bit is set while PyType_Ready() is in the process of initializing the type object.

Inheritance:

???

Py_TPFLAGS_HAVE_GC¶

This bit is set when the object supports garbage collection. If this bit is set, instances must be created using PyObject_GC_New and destroyed using PyObject_GC_Del(). More information in sectionSupporting Cyclic Garbage Collection. This bit also implies that the GC-related fields tp_traverse and tp_clear are present in the type object.

Inheritance:

Group: Py_TPFLAGS_HAVE_GC, tp_traverse, tp_clear

The Py_TPFLAGS_HAVE_GC flag bit is inherited together with the tp_traverse and tp_clearfields, i.e. if the Py_TPFLAGS_HAVE_GC flag bit is clear in the subtype and the tp_traverse andtp_clear fields in the subtype exist and have NULLvalues.

Py_TPFLAGS_DEFAULT¶

This is a bitmask of all the bits that pertain to the existence of certain fields in the type object and its extension structures. Currently, it includes the following bits: Py_TPFLAGS_HAVE_STACKLESS_EXTENSION.

Inheritance:

???

Py_TPFLAGS_METHOD_DESCRIPTOR¶

This bit indicates that objects behave like unbound methods.

If this flag is set for type(meth), then:

meth.__get__(obj, cls)(*args, **kwds) (with obj not None) must be equivalent to meth(obj, *args, **kwds).
meth.__get__(None, cls)(*args, **kwds)must be equivalent to meth(*args, **kwds).

This flag enables an optimization for typical method calls likeobj.meth(): it avoids creating a temporary “bound method” object forobj.meth.

Added in version 3.8.

Inheritance:

This flag is never inherited by types without thePy_TPFLAGS_IMMUTABLETYPE flag set. For extension types, it is inherited whenever tp_descr_get is inherited.

Py_TPFLAGS_MANAGED_DICT¶

This bit indicates that instances of the class have a ~object.__dict__attribute, and that the space for the dictionary is managed by the VM.

If this flag is set, Py_TPFLAGS_HAVE_GC should also be set.

The type traverse function must call PyObject_VisitManagedDict()and its clear function must call PyObject_ClearManagedDict().

Added in version 3.12.

Inheritance:

This flag is inherited unless thetp_dictoffset field is set in a superclass.

Py_TPFLAGS_MANAGED_WEAKREF¶

This bit indicates that instances of the class should be weakly referenceable.

Added in version 3.12.

Inheritance:

This flag is inherited unless thetp_weaklistoffset field is set in a superclass.

Py_TPFLAGS_ITEMS_AT_END¶

Only usable with variable-size types, i.e. ones with non-zerotp_itemsize.

Indicates that the variable-sized portion of an instance of this type is at the end of the instance’s memory area, at an offset ofPy_TYPE(obj)->tp_basicsize (which may be different in each subclass).

When setting this flag, be sure that all superclasses either use this memory layout, or are not variable-sized. Python does not check this.

Added in version 3.12.

Inheritance:

This flag is inherited.

Py_TPFLAGS_LONG_SUBCLASS¶

Py_TPFLAGS_LIST_SUBCLASS¶

Py_TPFLAGS_TUPLE_SUBCLASS¶

Py_TPFLAGS_BYTES_SUBCLASS¶

Py_TPFLAGS_UNICODE_SUBCLASS¶

Py_TPFLAGS_DICT_SUBCLASS¶

Py_TPFLAGS_BASE_EXC_SUBCLASS¶

Py_TPFLAGS_TYPE_SUBCLASS¶

These flags are used by functions such asPyLong_Check() to quickly determine if a type is a subclass of a built-in type; such specific checks are faster than a generic check, like PyObject_IsInstance(). Custom types that inherit from built-ins should have their tp_flagsset appropriately, or the code that interacts with such types will behave differently depending on what kind of check is used.

Py_TPFLAGS_HAVE_FINALIZE¶

This bit is set when the tp_finalize slot is present in the type structure.

Added in version 3.4.

Deprecated since version 3.8: This flag isn’t necessary anymore, as the interpreter assumes thetp_finalize slot is always present in the type structure.

Py_TPFLAGS_HAVE_VECTORCALL¶

This bit is set when the class implements the vectorcall protocol. See tp_vectorcall_offset for details.

Inheritance:

This bit is inherited if tp_call is also inherited.

Added in version 3.9.

Changed in version 3.12: This flag is now removed from a class when the class’s__call__() method is reassigned.

This flag can now be inherited by mutable classes.

Py_TPFLAGS_IMMUTABLETYPE¶

This bit is set for type objects that are immutable: type attributes cannot be set nor deleted.

PyType_Ready() automatically applies this flag tostatic types.

Inheritance:

This flag is not inherited.

Added in version 3.10.

Py_TPFLAGS_DISALLOW_INSTANTIATION¶

Disallow creating instances of the type: settp_new to NULL and don’t create the __new__key in the type dictionary.

The flag must be set before creating the type, not after. For example, it must be set before PyType_Ready() is called on the type.

The flag is set automatically on static types iftp_base is NULL or &PyBaseObject_Type andtp_new is NULL.

Inheritance:

This flag is not inherited. However, subclasses will not be instantiable unless they provide a non-NULL tp_new (which is only possible via the C API).

Note

To disallow instantiating a class directly but allow instantiating its subclasses (e.g. for an abstract base class), do not use this flag. Instead, make tp_new only succeed for subclasses.

Added in version 3.10.

Py_TPFLAGS_MAPPING¶

This bit indicates that instances of the class may match mapping patterns when used as the subject of a match block. It is automatically set when registering or subclassing collections.abc.Mapping, and unset when registering collections.abc.Sequence.

Note

Py_TPFLAGS_MAPPING and Py_TPFLAGS_SEQUENCE are mutually exclusive; it is an error to enable both flags simultaneously.

Inheritance:

This flag is inherited by types that do not already setPy_TPFLAGS_SEQUENCE.

See also

PEP 634 – Structural Pattern Matching: Specification

Added in version 3.10.

Py_TPFLAGS_VALID_VERSION_TAG¶

Internal. Do not set or unset this flag. To indicate that a class has changed call PyType_Modified()

Warning

This flag is present in header files, but is not be used. It will be removed in a future version of CPython

const char *PyTypeObject.tp_doc¶

An optional pointer to a NUL-terminated C string giving the docstring for this type object. This is exposed as the __doc__ attribute on the type and instances of the type.

Inheritance:

This field is not inherited by subtypes.

traverseproc PyTypeObject.tp_traverse¶

An optional pointer to a traversal function for the garbage collector. This is only used if the Py_TPFLAGS_HAVE_GC flag bit is set. The signature is:

int tp_traverse(PyObject *self, visitproc visit, void *arg);

More information about Python’s garbage collection scheme can be found in section Supporting Cyclic Garbage Collection.

The tp_traverse pointer is used by the garbage collector to detect reference cycles. A typical implementation of a tp_traverse function simply calls Py_VISIT() on each of the instance’s members that are Python objects that the instance owns. For example, this is function local_traverse() from the_thread extension module:

static int local_traverse(localobject *self, visitproc visit, void *arg) { Py_VISIT(self->args); Py_VISIT(self->kw); Py_VISIT(self->dict); return 0; }

Note that Py_VISIT() is called only on those members that can participate in reference cycles. Although there is also a self->key member, it can only be NULL or a Python string and therefore cannot be part of a reference cycle.

On the other hand, even if you know a member can never be part of a cycle, as a debugging aid you may want to visit it anyway just so the gc module’sget_referents() function will include it.

Heap types (Py_TPFLAGS_HEAPTYPE) must visit their type with:

It is only needed since Python 3.9. To support Python 3.8 and older, this line must be conditional:

#if PY_VERSION_HEX >= 0x03090000 Py_VISIT(Py_TYPE(self)); #endif

If the Py_TPFLAGS_MANAGED_DICT bit is set in thetp_flags field, the traverse function must callPyObject_VisitManagedDict() like this:

PyObject_VisitManagedDict((PyObject*)self, visit, arg);

Warning

When implementing tp_traverse, only the members that the instance owns (by having strong references to them) must be visited. For instance, if an object supports weak references via thetp_weaklist slot, the pointer supporting the linked list (what tp_weaklist points to) must not be visited as the instance does not directly own the weak references to itself (the weakreference list is there to support the weak reference machinery, but the instance has no strong reference to the elements inside it, as they are allowed to be removed even if the instance is still alive).

Note that Py_VISIT() requires the visit and arg parameters tolocal_traverse() to have these specific names; don’t name them just anything.

Instances of heap-allocated types hold a reference to their type. Their traversal function must therefore either visitPy_TYPE(self), or delegate this responsibility by calling tp_traverse of another heap-allocated type (such as a heap-allocated superclass). If they do not, the type object may not be garbage-collected.

Changed in version 3.9: Heap-allocated types are expected to visit Py_TYPE(self) intp_traverse. In earlier versions of Python, due tobug 40217, doing this may lead to crashes in subclasses.

Inheritance:

Group: Py_TPFLAGS_HAVE_GC, tp_traverse, tp_clear

This field is inherited by subtypes together with tp_clear and thePy_TPFLAGS_HAVE_GC flag bit: the flag bit, tp_traverse, andtp_clear are all inherited from the base type if they are all zero in the subtype.

inquiry PyTypeObject.tp_clear¶

An optional pointer to a clear function for the garbage collector. This is only used if the Py_TPFLAGS_HAVE_GC flag bit is set. The signature is:

int tp_clear(PyObject *);

The tp_clear member function is used to break reference cycles in cyclic garbage detected by the garbage collector. Taken together, all tp_clearfunctions in the system must combine to break all reference cycles. This is subtle, and if in any doubt supply a tp_clear function. For example, the tuple type does not implement a tp_clear function, because it’s possible to prove that no reference cycle can be composed entirely of tuples. Therefore the tp_clear functions of other types must be sufficient to break any cycle containing a tuple. This isn’t immediately obvious, and there’s rarely a good reason to avoid implementing tp_clear.

Implementations of tp_clear should drop the instance’s references to those of its members that may be Python objects, and set its pointers to those members to NULL, as in the following example:

static int local_clear(localobject *self) { Py_CLEAR(self->key); Py_CLEAR(self->args); Py_CLEAR(self->kw); Py_CLEAR(self->dict); return 0; }

The Py_CLEAR() macro should be used, because clearing references is delicate: the reference to the contained object must not be released (via Py_DECREF()) until after the pointer to the contained object is set to NULL. This is because releasing the reference may cause the contained object to become trash, triggering a chain of reclamation activity that may include invoking arbitrary Python code (due to finalizers, or weakref callbacks, associated with the contained object). If it’s possible for such code to reference self again, it’s important that the pointer to the contained object be NULL at that time, so that self knows the contained object can no longer be used. ThePy_CLEAR() macro performs the operations in a safe order.

If the Py_TPFLAGS_MANAGED_DICT bit is set in thetp_flags field, the traverse function must callPyObject_ClearManagedDict() like this:

PyObject_ClearManagedDict((PyObject*)self);

Note that tp_clear is not always called before an instance is deallocated. For example, when reference counting is enough to determine that an object is no longer used, the cyclic garbage collector is not involved and tp_dealloc is called directly.

Because the goal of tp_clear functions is to break reference cycles, it’s not necessary to clear contained objects like Python strings or Python integers, which can’t participate in reference cycles. On the other hand, it may be convenient to clear all contained Python objects, and write the type’stp_dealloc function to invoke tp_clear.

More information about Python’s garbage collection scheme can be found in section Supporting Cyclic Garbage Collection.

Inheritance:

Group: Py_TPFLAGS_HAVE_GC, tp_traverse, tp_clear

This field is inherited by subtypes together with tp_traverse and thePy_TPFLAGS_HAVE_GC flag bit: the flag bit, tp_traverse, andtp_clear are all inherited from the base type if they are all zero in the subtype.

richcmpfunc PyTypeObject.tp_richcompare¶

An optional pointer to the rich comparison function, whose signature is:

PyObject *tp_richcompare(PyObject *self, PyObject *other, int op);

The first parameter is guaranteed to be an instance of the type that is defined by PyTypeObject.

The function should return the result of the comparison (usually Py_Trueor Py_False). If the comparison is undefined, it must returnPy_NotImplemented, if another error occurred it must return NULL and set an exception condition.

The following constants are defined to be used as the third argument fortp_richcompare and for PyObject_RichCompare():

Constant	Comparison
Py_LT¶	<
Py_LE¶	<=
Py_EQ¶	==
Py_NE¶	!=
Py_GT¶	>
Py_GE¶	>=

The following macro is defined to ease writing rich comparison functions:

Py_RETURN_RICHCOMPARE(VAL_A, VAL_B, op)¶

Return Py_True or Py_False from the function, depending on the result of a comparison. VAL_A and VAL_B must be orderable by C comparison operators (for example, they may be C ints or floats). The third argument specifies the requested operation, as for PyObject_RichCompare().

The returned value is a new strong reference.

On error, sets an exception and returns NULL from the function.

Added in version 3.7.

Inheritance:

Group: tp_hash, tp_richcompare

This field is inherited by subtypes together with tp_hash: a subtype inherits tp_richcompare and tp_hash when the subtype’s tp_richcompare and tp_hash are bothNULL.

Default:

PyBaseObject_Type provides a tp_richcompareimplementation, which may be inherited. However, if onlytp_hash is defined, not even the inherited function is used and instances of the type will not be able to participate in any comparisons.

Py_ssize_t PyTypeObject.tp_weaklistoffset¶

While this field is still supported, Py_TPFLAGS_MANAGED_WEAKREFshould be used instead, if at all possible.

If the instances of this type are weakly referenceable, this field is greater than zero and contains the offset in the instance structure of the weak reference list head (ignoring the GC header, if present); this offset is used byPyObject_ClearWeakRefs() and the PyWeakref_* functions. The instance structure needs to include a field of type PyObject* which is initialized to NULL.

Do not confuse this field with tp_weaklist; that is the list head for weak references to the type object itself.

It is an error to set both the Py_TPFLAGS_MANAGED_WEAKREF bit andtp_weaklistoffset.

Inheritance:

This field is inherited by subtypes, but see the rules listed below. A subtype may override this offset; this means that the subtype uses a different weak reference list head than the base type. Since the list head is always found viatp_weaklistoffset, this should not be a problem.

Default:

If the Py_TPFLAGS_MANAGED_WEAKREF bit is set in thetp_flags field, thentp_weaklistoffset will be set to a negative value, to indicate that it is unsafe to use this field.

getiterfunc PyTypeObject.tp_iter¶

An optional pointer to a function that returns an iterator for the object. Its presence normally signals that the instances of this type areiterable (although sequences may be iterable without this function).

This function has the same signature as PyObject_GetIter():

PyObject *tp_iter(PyObject *self);

Inheritance:

This field is inherited by subtypes.

iternextfunc PyTypeObject.tp_iternext¶

An optional pointer to a function that returns the next item in aniterator. The signature is:

PyObject *tp_iternext(PyObject *self);

When the iterator is exhausted, it must return NULL; a StopIterationexception may or may not be set. When another error occurs, it must returnNULL too. Its presence signals that the instances of this type are iterators.

Iterator types should also define the tp_iter function, and that function should return the iterator instance itself (not a new iterator instance).

This function has the same signature as PyIter_Next().

Inheritance:

This field is inherited by subtypes.

struct PyMethodDef *PyTypeObject.tp_methods¶

An optional pointer to a static NULL-terminated array of PyMethodDefstructures, declaring regular methods of this type.

For each entry in the array, an entry is added to the type’s dictionary (seetp_dict below) containing a method descriptor.

Inheritance:

This field is not inherited by subtypes (methods are inherited through a different mechanism).

struct PyMemberDef *PyTypeObject.tp_members¶

An optional pointer to a static NULL-terminated array of PyMemberDefstructures, declaring regular data members (fields or slots) of instances of this type.

For each entry in the array, an entry is added to the type’s dictionary (seetp_dict below) containing a member descriptor.

Inheritance:

This field is not inherited by subtypes (members are inherited through a different mechanism).

struct PyGetSetDef *PyTypeObject.tp_getset¶

An optional pointer to a static NULL-terminated array of PyGetSetDefstructures, declaring computed attributes of instances of this type.

For each entry in the array, an entry is added to the type’s dictionary (seetp_dict below) containing a getset descriptor.

Inheritance:

This field is not inherited by subtypes (computed attributes are inherited through a different mechanism).

PyTypeObject *PyTypeObject.tp_base¶

An optional pointer to a base type from which type properties are inherited. At this level, only single inheritance is supported; multiple inheritance require dynamically creating a type object by calling the metatype.

Note

Slot initialization is subject to the rules of initializing globals. C99 requires the initializers to be “address constants”. Function designators like PyType_GenericNew(), with implicit conversion to a pointer, are valid C99 address constants.

However, the unary ‘&’ operator applied to a non-static variable like PyBaseObject_Type is not required to produce an address constant. Compilers may support this (gcc does), MSVC does not. Both compilers are strictly standard conforming in this particular behavior.

Consequently, tp_base should be set in the extension module’s init function.

Inheritance:

This field is not inherited by subtypes (obviously).

Default:

This field defaults to &PyBaseObject_Type (which to Python programmers is known as the type object).

PyObject *PyTypeObject.tp_dict¶

The type’s dictionary is stored here by PyType_Ready().

This field should normally be initialized to NULL before PyType_Ready is called; it may also be initialized to a dictionary containing initial attributes for the type. Once PyType_Ready() has initialized the type, extra attributes for the type may be added to this dictionary only if they don’t correspond to overloaded operations (like __add__()). Once initialization for the type has finished, this field should be treated as read-only.

Some types may not store their dictionary in this slot. Use PyType_GetDict() to retrieve the dictionary for an arbitrary type.

Changed in version 3.12: Internals detail: For static builtin types, this is always NULL. Instead, the dict for such types is stored on PyInterpreterState. Use PyType_GetDict() to get the dict for an arbitrary type.

Inheritance:

This field is not inherited by subtypes (though the attributes defined in here are inherited through a different mechanism).

Default:

If this field is NULL, PyType_Ready() will assign a new dictionary to it.

Warning

It is not safe to use PyDict_SetItem() on or otherwise modifytp_dict with the dictionary C-API.

descrgetfunc PyTypeObject.tp_descr_get¶

An optional pointer to a “descriptor get” function.

The function signature is:

PyObject * tp_descr_get(PyObject *self, PyObject *obj, PyObject *type);

Inheritance:

This field is inherited by subtypes.

descrsetfunc PyTypeObject.tp_descr_set¶

An optional pointer to a function for setting and deleting a descriptor’s value.

The function signature is:

int tp_descr_set(PyObject *self, PyObject *obj, PyObject *value);

The value argument is set to NULL to delete the value.

Inheritance:

This field is inherited by subtypes.

Py_ssize_t PyTypeObject.tp_dictoffset¶

While this field is still supported, Py_TPFLAGS_MANAGED_DICT should be used instead, if at all possible.

If the instances of this type have a dictionary containing instance variables, this field is non-zero and contains the offset in the instances of the type of the instance variable dictionary; this offset is used byPyObject_GenericGetAttr().

Do not confuse this field with tp_dict; that is the dictionary for attributes of the type object itself.

The value specifies the offset of the dictionary from the start of the instance structure.

The tp_dictoffset should be regarded as write-only. To get the pointer to the dictionary call PyObject_GenericGetDict(). Calling PyObject_GenericGetDict() may need to allocate memory for the dictionary, so it is may be more efficient to call PyObject_GetAttr()when accessing an attribute on the object.

It is an error to set both the Py_TPFLAGS_MANAGED_DICT bit andtp_dictoffset.

Inheritance:

This field is inherited by subtypes. A subtype should not override this offset; doing so could be unsafe, if C code tries to access the dictionary at the previous offset. To properly support inheritance, use Py_TPFLAGS_MANAGED_DICT.

Default:

This slot has no default. For static types, if the field is NULL then no __dict__ gets created for instances.

If the Py_TPFLAGS_MANAGED_DICT bit is set in thetp_flags field, thentp_dictoffset will be set to -1, to indicate that it is unsafe to use this field.

initproc PyTypeObject.tp_init¶

An optional pointer to an instance initialization function.

This function corresponds to the __init__() method of classes. Like__init__(), it is possible to create an instance without calling__init__(), and it is possible to reinitialize an instance by calling its__init__() method again.

The function signature is:

int tp_init(PyObject *self, PyObject *args, PyObject *kwds);

The self argument is the instance to be initialized; the args and _kwds_arguments represent positional and keyword arguments of the call to__init__().

The tp_init function, if not NULL, is called when an instance is created normally by calling its type, after the type’s tp_new function has returned an instance of the type. If the tp_new function returns an instance of some other type that is not a subtype of the original type, notp_init function is called; if tp_new returns an instance of a subtype of the original type, the subtype’s tp_init is called.

Returns 0 on success, -1 and sets an exception on error.

Inheritance:

This field is inherited by subtypes.

Default:

For static types this field does not have a default.

allocfunc PyTypeObject.tp_alloc¶

An optional pointer to an instance allocation function.

The function signature is:

PyObject *tp_alloc(PyTypeObject *self, Py_ssize_t nitems);

Inheritance:

This field is inherited by static subtypes, but not by dynamic subtypes (subtypes created by a class statement).

Default:

For dynamic subtypes, this field is always set toPyType_GenericAlloc(), to force a standard heap allocation strategy.

For static subtypes, PyBaseObject_Type usesPyType_GenericAlloc(). That is the recommended value for all statically defined types.

newfunc PyTypeObject.tp_new¶

An optional pointer to an instance creation function.

The function signature is:

PyObject *tp_new(PyTypeObject *subtype, PyObject *args, PyObject *kwds);

The subtype argument is the type of the object being created; the args and_kwds_ arguments represent positional and keyword arguments of the call to the type. Note that subtype doesn’t have to equal the type whose tp_newfunction is called; it may be a subtype of that type (but not an unrelated type).

The tp_new function should call subtype->tp_alloc(subtype, nitems)to allocate space for the object, and then do only as much further initialization as is absolutely necessary. Initialization that can safely be ignored or repeated should be placed in the tp_init handler. A good rule of thumb is that for immutable types, all initialization should take place in tp_new, while for mutable types, most initialization should be deferred to tp_init.

Set the Py_TPFLAGS_DISALLOW_INSTANTIATION flag to disallow creating instances of the type in Python.

Inheritance:

This field is inherited by subtypes, except it is not inherited bystatic types whose tp_baseis NULL or &PyBaseObject_Type.

Default:

For static types this field has no default. This means if the slot is defined as NULL, the type cannot be called to create new instances; presumably there is some other way to create instances, like a factory function.

freefunc PyTypeObject.tp_free¶

An optional pointer to an instance deallocation function. Its signature is:

void tp_free(void *self);

An initializer that is compatible with this signature is PyObject_Free().

Inheritance:

This field is inherited by static subtypes, but not by dynamic subtypes (subtypes created by a class statement)

Default:

In dynamic subtypes, this field is set to a deallocator suitable to match PyType_GenericAlloc() and the value of thePy_TPFLAGS_HAVE_GC flag bit.

For static subtypes, PyBaseObject_Type uses PyObject_Del().

inquiry PyTypeObject.tp_is_gc¶

An optional pointer to a function called by the garbage collector.

The garbage collector needs to know whether a particular object is collectible or not. Normally, it is sufficient to look at the object’s type’stp_flags field, and check the Py_TPFLAGS_HAVE_GC flag bit. But some types have a mixture of statically and dynamically allocated instances, and the statically allocated instances are not collectible. Such types should define this function; it should return 1 for a collectible instance, and0 for a non-collectible instance. The signature is:

int tp_is_gc(PyObject *self);

(The only example of this are types themselves. The metatype,PyType_Type, defines this function to distinguish between statically and dynamically allocated types.)

Inheritance:

This field is inherited by subtypes.

Default:

This slot has no default. If this field is NULL,Py_TPFLAGS_HAVE_GC is used as the functional equivalent.

PyObject *PyTypeObject.tp_bases¶

Tuple of base types.

This field should be set to NULL and treated as read-only. Python will fill it in when the type is initialized.

For dynamically created classes, the Py_tp_bases slot can be used instead of the bases argument of PyType_FromSpecWithBases(). The argument form is preferred.

Warning

Multiple inheritance does not work well for statically defined types. If you set tp_bases to a tuple, Python will not raise an error, but some slots will only be inherited from the first base.

Inheritance:

This field is not inherited.

PyObject *PyTypeObject.tp_mro¶

Tuple containing the expanded set of base types, starting with the type itself and ending with object, in Method Resolution Order.

This field should be set to NULL and treated as read-only. Python will fill it in when the type is initialized.

Inheritance:

This field is not inherited; it is calculated fresh byPyType_Ready().

PyObject *PyTypeObject.tp_cache¶

Unused. Internal use only.

Inheritance:

This field is not inherited.

void *PyTypeObject.tp_subclasses¶

A collection of subclasses. Internal use only. May be an invalid pointer.

To get a list of subclasses, call the Python method__subclasses__().

Changed in version 3.12: For some types, this field does not hold a valid PyObject*. The type was changed to void* to indicate this.

Inheritance:

This field is not inherited.

PyObject *PyTypeObject.tp_weaklist¶

Weak reference list head, for weak references to this type object. Not inherited. Internal use only.

Changed in version 3.12: Internals detail: For the static builtin types this is always NULL, even if weakrefs are added. Instead, the weakrefs for each are stored on PyInterpreterState. Use the public C-API or the internal_PyObject_GET_WEAKREFS_LISTPTR() macro to avoid the distinction.

Inheritance:

This field is not inherited.

destructor PyTypeObject.tp_del¶

This field is deprecated. Use tp_finalize instead.

unsigned int PyTypeObject.tp_version_tag¶

Used to index into the method cache. Internal use only.

Inheritance:

This field is not inherited.

destructor PyTypeObject.tp_finalize¶

An optional pointer to an instance finalization function. Its signature is:

void tp_finalize(PyObject *self);

If tp_finalize is set, the interpreter calls it once when finalizing an instance. It is called either from the garbage collector (if the instance is part of an isolated reference cycle) or just before the object is deallocated. Either way, it is guaranteed to be called before attempting to break reference cycles, ensuring that it finds the object in a sane state.

tp_finalize should not mutate the current exception status; therefore, a recommended way to write a non-trivial finalizer is:

static void local_finalize(PyObject self) { / Save the current exception, if any. */ PyObject *exc = PyErr_GetRaisedException();

/* ... */

/* Restore the saved exception. */
PyErr_SetRaisedException(exc);

}

Inheritance:

This field is inherited by subtypes.

Added in version 3.4.

Changed in version 3.8: Before version 3.8 it was necessary to set thePy_TPFLAGS_HAVE_FINALIZE flags bit in order for this field to be used. This is no longer required.

Static Types¶

Traditionally, types defined in C code are static, that is, a static PyTypeObject structure is defined directly in code and initialized using PyType_Ready().

This results in types that are limited relative to types defined in Python:

Static types are limited to one base, i.e. they cannot use multiple inheritance.
Static type objects (but not necessarily their instances) are immutable. It is not possible to add or modify the type object’s attributes from Python.
Static type objects are shared acrosssub-interpreters, so they should not include any subinterpreter-specific state.

Also, since PyTypeObject is only part of the Limited API as an opaque struct, any extension modules using static types must be compiled for a specific Python minor version.

Heap Types¶

An alternative to static types is heap-allocated types, or heap types for short, which correspond closely to classes created by Python’s class statement. Heap types have the Py_TPFLAGS_HEAPTYPEflag set.

This is done by filling a PyType_Spec structure and callingPyType_FromSpec(), PyType_FromSpecWithBases(),PyType_FromModuleAndSpec(), or PyType_FromMetaclass().

Number Object Structures¶

type PyNumberMethods¶

This structure holds pointers to the functions which an object uses to implement the number protocol. Each function is used by the function of similar name documented in the Number Protocol section.

Here is the structure definition:

typedef struct { binaryfunc nb_add; binaryfunc nb_subtract; binaryfunc nb_multiply; binaryfunc nb_remainder; binaryfunc nb_divmod; ternaryfunc nb_power; unaryfunc nb_negative; unaryfunc nb_positive; unaryfunc nb_absolute; inquiry nb_bool; unaryfunc nb_invert; binaryfunc nb_lshift; binaryfunc nb_rshift; binaryfunc nb_and; binaryfunc nb_xor; binaryfunc nb_or; unaryfunc nb_int; void *nb_reserved; unaryfunc nb_float;

 binaryfunc nb_inplace_add;
 binaryfunc nb_inplace_subtract;
 binaryfunc nb_inplace_multiply;
 binaryfunc nb_inplace_remainder;
 ternaryfunc nb_inplace_power;
 binaryfunc nb_inplace_lshift;
 binaryfunc nb_inplace_rshift;
 binaryfunc nb_inplace_and;
 binaryfunc nb_inplace_xor;
 binaryfunc nb_inplace_or;

 binaryfunc nb_floor_divide;
 binaryfunc nb_true_divide;
 binaryfunc nb_inplace_floor_divide;
 binaryfunc nb_inplace_true_divide;

 unaryfunc nb_index;

 binaryfunc nb_matrix_multiply;
 binaryfunc nb_inplace_matrix_multiply;

} PyNumberMethods;

Note

Binary and ternary functions must check the type of all their operands, and implement the necessary conversions (at least one of the operands is an instance of the defined type). If the operation is not defined for the given operands, binary and ternary functions must returnPy_NotImplemented, if another error occurred they must return NULLand set an exception.

Note

The nb_reserved field should always be NULL. It was previously called nb_long, and was renamed in Python 3.0.1.

binaryfunc PyNumberMethods.nb_add¶

binaryfunc PyNumberMethods.nb_subtract¶

binaryfunc PyNumberMethods.nb_multiply¶

binaryfunc PyNumberMethods.nb_remainder¶

binaryfunc PyNumberMethods.nb_divmod¶

ternaryfunc PyNumberMethods.nb_power¶

unaryfunc PyNumberMethods.nb_negative¶

unaryfunc PyNumberMethods.nb_positive¶

unaryfunc PyNumberMethods.nb_absolute¶

inquiry PyNumberMethods.nb_bool¶

unaryfunc PyNumberMethods.nb_invert¶

binaryfunc PyNumberMethods.nb_lshift¶

binaryfunc PyNumberMethods.nb_rshift¶

binaryfunc PyNumberMethods.nb_and¶

binaryfunc PyNumberMethods.nb_xor¶

binaryfunc PyNumberMethods.nb_or¶

unaryfunc PyNumberMethods.nb_int¶

void *PyNumberMethods.nb_reserved¶

unaryfunc PyNumberMethods.nb_float¶

binaryfunc PyNumberMethods.nb_inplace_add¶

binaryfunc PyNumberMethods.nb_inplace_subtract¶

binaryfunc PyNumberMethods.nb_inplace_multiply¶

binaryfunc PyNumberMethods.nb_inplace_remainder¶

ternaryfunc PyNumberMethods.nb_inplace_power¶

binaryfunc PyNumberMethods.nb_inplace_lshift¶

binaryfunc PyNumberMethods.nb_inplace_rshift¶

binaryfunc PyNumberMethods.nb_inplace_and¶

binaryfunc PyNumberMethods.nb_inplace_xor¶

binaryfunc PyNumberMethods.nb_inplace_or¶

binaryfunc PyNumberMethods.nb_floor_divide¶

binaryfunc PyNumberMethods.nb_true_divide¶

binaryfunc PyNumberMethods.nb_inplace_floor_divide¶

binaryfunc PyNumberMethods.nb_inplace_true_divide¶

unaryfunc PyNumberMethods.nb_index¶

binaryfunc PyNumberMethods.nb_matrix_multiply¶

binaryfunc PyNumberMethods.nb_inplace_matrix_multiply¶

Mapping Object Structures¶

type PyMappingMethods¶

This structure holds pointers to the functions which an object uses to implement the mapping protocol. It has three members:

lenfunc PyMappingMethods.mp_length¶

This function is used by PyMapping_Size() andPyObject_Size(), and has the same signature. This slot may be set toNULL if the object has no defined length.

binaryfunc PyMappingMethods.mp_subscript¶

This function is used by PyObject_GetItem() andPySequence_GetSlice(), and has the same signature asPyObject_GetItem(). This slot must be filled for thePyMapping_Check() function to return 1, it can be NULLotherwise.

objobjargproc PyMappingMethods.mp_ass_subscript¶

This function is used by PyObject_SetItem(),PyObject_DelItem(), PySequence_SetSlice() andPySequence_DelSlice(). It has the same signature asPyObject_SetItem(), but v can also be set to NULL to delete an item. If this slot is NULL, the object does not support item assignment and deletion.

Sequence Object Structures¶

type PySequenceMethods¶

This structure holds pointers to the functions which an object uses to implement the sequence protocol.

lenfunc PySequenceMethods.sq_length¶

This function is used by PySequence_Size() andPyObject_Size(), and has the same signature. It is also used for handling negative indices via the sq_itemand the sq_ass_item slots.

binaryfunc PySequenceMethods.sq_concat¶

This function is used by PySequence_Concat() and has the same signature. It is also used by the + operator, after trying the numeric addition via the nb_add slot.

ssizeargfunc PySequenceMethods.sq_repeat¶

This function is used by PySequence_Repeat() and has the same signature. It is also used by the * operator, after trying numeric multiplication via the nb_multiply slot.

ssizeargfunc PySequenceMethods.sq_item¶

This function is used by PySequence_GetItem() and has the same signature. It is also used by PyObject_GetItem(), after trying the subscription via the mp_subscript slot. This slot must be filled for the PySequence_Check()function to return 1, it can be NULL otherwise.

Negative indexes are handled as follows: if the sq_length slot is filled, it is called and the sequence length is used to compute a positive index which is passed to sq_item. If sq_length is NULL, the index is passed as is to the function.

ssizeobjargproc PySequenceMethods.sq_ass_item¶

This function is used by PySequence_SetItem() and has the same signature. It is also used by PyObject_SetItem() andPyObject_DelItem(), after trying the item assignment and deletion via the mp_ass_subscript slot. This slot may be left to NULL if the object does not support item assignment and deletion.

objobjproc PySequenceMethods.sq_contains¶

This function may be used by PySequence_Contains() and has the same signature. This slot may be left to NULL, in this casePySequence_Contains() simply traverses the sequence until it finds a match.

binaryfunc PySequenceMethods.sq_inplace_concat¶

This function is used by PySequence_InPlaceConcat() and has the same signature. It should modify its first operand, and return it. This slot may be left to NULL, in this case PySequence_InPlaceConcat()will fall back to PySequence_Concat(). It is also used by the augmented assignment +=, after trying numeric in-place addition via the nb_inplace_add slot.

ssizeargfunc PySequenceMethods.sq_inplace_repeat¶

This function is used by PySequence_InPlaceRepeat() and has the same signature. It should modify its first operand, and return it. This slot may be left to NULL, in this case PySequence_InPlaceRepeat()will fall back to PySequence_Repeat(). It is also used by the augmented assignment *=, after trying numeric in-place multiplication via the nb_inplace_multiply slot.

Buffer Object Structures¶

type PyBufferProcs¶

This structure holds pointers to the functions required by theBuffer protocol. The protocol defines how an exporter object can expose its internal data to consumer objects.

getbufferproc PyBufferProcs.bf_getbuffer¶

The signature of this function is:

int (PyObject *exporter, Py_buffer *view, int flags);

Handle a request to exporter to fill in view as specified by flags. Except for point (3), an implementation of this function MUST take these steps:

Check if the request can be met. If not, raise BufferError, set view->obj to NULL and return -1.
Fill in the requested fields.
Increment an internal counter for the number of exports.
Set view->obj to exporter and increment view->obj.
Return 0.

If exporter is part of a chain or tree of buffer providers, two main schemes can be used:

Re-export: Each member of the tree acts as the exporting object and sets view->obj to a new reference to itself.
Redirect: The buffer request is redirected to the root object of the tree. Here, view->obj will be a new reference to the root object.

The individual fields of view are described in sectionBuffer structure, the rules how an exporter must react to specific requests are in sectionBuffer request types.

All memory pointed to in the Py_buffer structure belongs to the exporter and must remain valid until there are no consumers left.format, shape,strides, suboffsetsand internalare read-only for the consumer.

PyBuffer_FillInfo() provides an easy way of exposing a simple bytes buffer while dealing correctly with all request types.

PyObject_GetBuffer() is the interface for the consumer that wraps this function.

releasebufferproc PyBufferProcs.bf_releasebuffer¶

The signature of this function is:

void (PyObject *exporter, Py_buffer *view);

Handle a request to release the resources of the buffer. If no resources need to be released, PyBufferProcs.bf_releasebuffer may beNULL. Otherwise, a standard implementation of this function will take these optional steps:

Decrement an internal counter for the number of exports.
If the counter is 0, free all memory associated with view.

The exporter MUST use the internal field to keep track of buffer-specific resources. This field is guaranteed to remain constant, while a consumer MAY pass a copy of the original buffer as the_view_ argument.

This function MUST NOT decrement view->obj, since that is done automatically in PyBuffer_Release() (this scheme is useful for breaking reference cycles).

PyBuffer_Release() is the interface for the consumer that wraps this function.

Async Object Structures¶

Added in version 3.5.

type PyAsyncMethods¶

This structure holds pointers to the functions required to implementawaitable and asynchronous iterator objects.

Here is the structure definition:

typedef struct { unaryfunc am_await; unaryfunc am_aiter; unaryfunc am_anext; sendfunc am_send; } PyAsyncMethods;

unaryfunc PyAsyncMethods.am_await¶

The signature of this function is:

PyObject *am_await(PyObject *self);

The returned object must be an iterator, i.e. PyIter_Check()must return 1 for it.

This slot may be set to NULL if an object is not an awaitable.

unaryfunc PyAsyncMethods.am_aiter¶

The signature of this function is:

PyObject *am_aiter(PyObject *self);

Must return an asynchronous iterator object. See __anext__() for details.

This slot may be set to NULL if an object does not implement asynchronous iteration protocol.

unaryfunc PyAsyncMethods.am_anext¶

The signature of this function is:

PyObject *am_anext(PyObject *self);

Must return an awaitable object. See __anext__() for details. This slot may be set to NULL.

sendfunc PyAsyncMethods.am_send¶

The signature of this function is:

PySendResult am_send(PyObject *self, PyObject *arg, PyObject **result);

See PyIter_Send() for details. This slot may be set to NULL.

Added in version 3.10.

Slot Type typedefs¶

typedef PyObject *(*allocfunc)(PyTypeObject *cls, Py_ssize_t nitems)¶

Part of the Stable ABI.

The purpose of this function is to separate memory allocation from memory initialization. It should return a pointer to a block of memory of adequate length for the instance, suitably aligned, and initialized to zeros, but withob_refcnt set to 1 and ob_type set to the type argument. If the type’s tp_itemsize is non-zero, the object’s ob_size field should be initialized to nitems and the length of the allocated memory block should be tp_basicsize + nitems*tp_itemsize, rounded up to a multiple ofsizeof(void*); otherwise, nitems is not used and the length of the block should be tp_basicsize.

This function should not do any other instance initialization, not even to allocate additional memory; that should be done by tp_new.

typedef void (*destructor)(PyObject*)¶

Part of the Stable ABI.

typedef void (*freefunc)(void*)¶

See tp_free.

typedef PyObject *(*newfunc)(PyTypeObject*, PyObject*, PyObject*)¶

Part of the Stable ABI.

See tp_new.

typedef int (*initproc)(PyObject*, PyObject*, PyObject*)¶

Part of the Stable ABI.

See tp_init.

typedef PyObject *(*reprfunc)(PyObject*)¶

Part of the Stable ABI.

See tp_repr.

typedef PyObject *(*getattrfunc)(PyObject *self, char *attr)¶

Part of the Stable ABI.

Return the value of the named attribute for the object.

typedef int (*setattrfunc)(PyObject *self, char *attr, PyObject *value)¶

Part of the Stable ABI.

Set the value of the named attribute for the object. The value argument is set to NULL to delete the attribute.

typedef PyObject *(*getattrofunc)(PyObject *self, PyObject *attr)¶

Part of the Stable ABI.

Return the value of the named attribute for the object.

See tp_getattro.

typedef int (*setattrofunc)(PyObject *self, PyObject *attr, PyObject *value)¶

Part of the Stable ABI.

Set the value of the named attribute for the object. The value argument is set to NULL to delete the attribute.

See tp_setattro.

typedef PyObject *(*descrgetfunc)(PyObject*, PyObject*, PyObject*)¶

Part of the Stable ABI.

See tp_descr_get.

typedef int (*descrsetfunc)(PyObject*, PyObject*, PyObject*)¶

Part of the Stable ABI.

See tp_descr_set.

typedef Py_hash_t (*hashfunc)(PyObject*)¶

Part of the Stable ABI.

See tp_hash.

typedef PyObject *(*richcmpfunc)(PyObject*, PyObject*, int)¶

Part of the Stable ABI.

See tp_richcompare.

typedef PyObject *(*getiterfunc)(PyObject*)¶

Part of the Stable ABI.

See tp_iter.

typedef PyObject *(*iternextfunc)(PyObject*)¶

Part of the Stable ABI.

See tp_iternext.

typedef Py_ssize_t (*lenfunc)(PyObject*)¶

Part of the Stable ABI.

typedef int (*getbufferproc)(PyObject*, Py_buffer*, int)¶

Part of the Stable ABI since version 3.12.

typedef void (*releasebufferproc)(PyObject*, Py_buffer*)¶

Part of the Stable ABI since version 3.12.

typedef PyObject *(*unaryfunc)(PyObject*)¶

Part of the Stable ABI.

typedef PyObject *(*binaryfunc)(PyObject*, PyObject*)¶

Part of the Stable ABI.

typedef PySendResult (*sendfunc)(PyObject*, PyObject*, PyObject**)¶

See am_send.

typedef PyObject *(*ternaryfunc)(PyObject*, PyObject*, PyObject*)¶

Part of the Stable ABI.

typedef PyObject *(*ssizeargfunc)(PyObject*, Py_ssize_t)¶

Part of the Stable ABI.

typedef int (*ssizeobjargproc)(PyObject*, Py_ssize_t, PyObject*)¶

Part of the Stable ABI.

typedef int (*objobjproc)(PyObject*, PyObject*)¶

Part of the Stable ABI.

typedef int (*objobjargproc)(PyObject*, PyObject*, PyObject*)¶

Part of the Stable ABI.

Examples¶

The following are simple examples of Python type definitions. They include common usage you may encounter. Some demonstrate tricky corner cases. For more examples, practical info, and a tutorial, seeDefining Extension Types: Tutorial and Defining Extension Types: Assorted Topics.

A basic static type:

typedef struct { PyObject_HEAD const char *data; } MyObject;

You may also find older code (especially in the CPython code base) with a more verbose initializer:

static PyTypeObject MyObject_Type = { PyVarObject_HEAD_INIT(NULL, 0) "mymod.MyObject", /* tp_name / sizeof(MyObject), / tp_basicsize / 0, / tp_itemsize / (destructor)myobj_dealloc, / tp_dealloc / 0, / tp_vectorcall_offset / 0, / tp_getattr / 0, / tp_setattr / 0, / tp_as_async / (reprfunc)myobj_repr, / tp_repr / 0, / tp_as_number / 0, / tp_as_sequence / 0, / tp_as_mapping / 0, / tp_hash / 0, / tp_call / 0, / tp_str / 0, / tp_getattro / 0, / tp_setattro / 0, / tp_as_buffer / 0, / tp_flags / PyDoc_STR("My objects"), / tp_doc / 0, / tp_traverse / 0, / tp_clear / 0, / tp_richcompare / 0, / tp_weaklistoffset / 0, / tp_iter / 0, / tp_iternext / 0, / tp_methods / 0, / tp_members / 0, / tp_getset / 0, / tp_base / 0, / tp_dict / 0, / tp_descr_get / 0, / tp_descr_set / 0, / tp_dictoffset / 0, / tp_init / 0, / tp_alloc / myobj_new, / tp_new */ };

A type that supports weakrefs, instance dicts, and hashing:

typedef struct { PyObject_HEAD const char *data; } MyObject;

static PyTypeObject MyObject_Type = { PyVarObject_HEAD_INIT(NULL, 0) .tp_name = "mymod.MyObject", .tp_basicsize = sizeof(MyObject), .tp_doc = PyDoc_STR("My objects"), .tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_MANAGED_DICT | Py_TPFLAGS_MANAGED_WEAKREF, .tp_new = myobj_new, .tp_traverse = (traverseproc)myobj_traverse, .tp_clear = (inquiry)myobj_clear, .tp_alloc = PyType_GenericNew, .tp_dealloc = (destructor)myobj_dealloc, .tp_repr = (reprfunc)myobj_repr, .tp_hash = (hashfunc)myobj_hash, .tp_richcompare = PyBaseObject_Type.tp_richcompare, };

A str subclass that cannot be subclassed and cannot be called to create instances (e.g. uses a separate factory func) usingPy_TPFLAGS_DISALLOW_INSTANTIATION flag:

typedef struct { PyUnicodeObject raw; char *extra; } MyStr;

static PyTypeObject MyStr_Type = { PyVarObject_HEAD_INIT(NULL, 0) .tp_name = "mymod.MyStr", .tp_basicsize = sizeof(MyStr), .tp_base = NULL, // set to &PyUnicode_Type in module init .tp_doc = PyDoc_STR("my custom str"), .tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_DISALLOW_INSTANTIATION, .tp_repr = (reprfunc)myobj_repr, };

The simplest static type with fixed-length instances:

typedef struct { PyObject_HEAD } MyObject;

static PyTypeObject MyObject_Type = { PyVarObject_HEAD_INIT(NULL, 0) .tp_name = "mymod.MyObject", };

The simplest static type with variable-length instances:

typedef struct { PyObject_VAR_HEAD const char *data[1]; } MyObject;

static PyTypeObject MyObject_Type = { PyVarObject_HEAD_INIT(NULL, 0) .tp_name = "mymod.MyObject", .tp_basicsize = sizeof(MyObject) - sizeof(char *), .tp_itemsize = sizeof(char *), };